Journal of Lipid Research, Vol 23, 1009-1019, Copyright © 1982 by Lipid Research, Inc.
A re-examination of the fate of glyceride-glycerol in neutral lipid absorption and transport
CM Mansbach 2d and S Parthasarathy
Conventional ideas concerning the unidirectional movement of
triacylglycerol from intestinal lumen to lymph with sn-2- monoacylglycerol
being the major glyceride-glycerol precursor were challenged by our finding
that steady state specific activities of radiolabeled triacylglycerol
(glyceryl moiety) in the intestinal mucosa and lumen were greatly reduced
as compared to the specific activity of intraduodenally infused
triacylglycerol. Investigation of the point at which the radiolabel was
diluted was performed in mesenteric lymph duct- cannulated rats with a
duodenal cannula through which trioleoyl[3H]glycerol was constantly
infused. Both within the bowel lumen and in the intestinal mucosa,
monoacylglycerol, diacylglycerol, and triacylglycerol specific activities
were 31% or less of the specific activity of the infusate; chylomicron
triacylglycerol specific activity was 75%. Efflux of neutral lipid from the
mucosa into the bowel lumen was directly demonstrated by finding that when
3H glucose was injected intraperitoneally during triolein infusion, luminal
triacylglycerol had a higher specific activity than was present in the
mucosa. We conclude that there are two pools of mucosal triacylglycerol.
One is rapidly transported and derives most of its glyceride-glycerol from
luminal monoacylglycerol. The second is slowly transported; it derives its
glyceride-glycerol mainly from endogenous sources and may efflux back into
the bowel lumen.